Encyclopedia of Associations: National Organizations of the U.S. -
"Comprehensive source of detailed information concerning nonprofit American membership organizations of national scope. Covers more than 23,000 organizations in categories such as trade, business, and commercial; legal, governmental, public administration, and military; cultural; educational; veterans, hereditary, and patriotic; athletic and sports; fan clubs, and many more."

If you would like to browse, click the Publications link at the top of the Gale Directory Library screen, then click the List All link, select either publication, then click Search (no search terms needed).